The zirconocene complex [Cp2ZrMe](+) reacts with 2,4-dimethyl-1-pentene to give methane and the allyl complex [Cp2Zr((eta)3+ CH2C(CH2CHMe2)CH2)](+). The reaction involves as an intermediate the unprecedented alkyl (eta)1-alkene complex [Cp2Zr(Me) ((eta)1+CH2CMeCH2CHMe2)](+), in which C(2) is essentially carbocationic and the C(1)-C(2) bond order is sufficiently low that rotation about it occurs. The hydrogen atoms of the methyl group on C(2) are sufficiently acidic that proton transfer to the Zr-Me group occurs to generate the allylic product. It seems likely that the chemistry described here provides a rationale for deactivation of propene polymerization catalysts since the normal products of chain transfer, polymers with vinylidene end groups, should form allylic species in the same way.